1. Field Of The Invention
This invention relates to an improvement in steam power plants for the generation of electricity, and in particular to reducing feed water requirements and condenser complexity by mechanically compressing power turbine exhaust steam to be recycled to the turbine.
2. Description of the Prior Art
Although there are many variations of controls and operating elements in steam power plants, the basic elements include a thermal steam source, steam turbines, generators, and one or more condensers to reclaim the turbine exhaust as hot feed water. Various pressure controls and the recycling of dry turbine exhaust steam to super heater tubes are well known variations to the basic power plant to control operating conditions and increase thermal efficiency.
Re-compression of turbine exhaust steam by mechanical means to be recycled to the power turbine has not been previously been included in such systems, as the mechanical energy used in compression cannot be entirely extracted as work energy by the turbine, resulting in a net energy loss. However, particularily with nuclear fueled power plants, the large quantities of cooling water and boiler feed water required are, in many locations, more critical limitations than thermal efficiency. Consequently, in such locations it may be advantageous to sacrifice optimum thermal efficiency in order to reduce water requirements. An objective of the present invention is to reduce feed water requirements in the steam loop, and by so doing, also reduce the size and complexity of the condensers.
Although mechanically compressed turbine exhaust steam has not previously been used for this purpose, it has been known to mechanically compress steam engine exhaust for auxiliary purposes, such as described in U.S. Pat. No. 1,066,348 to G. T. Voorhees, which describes mechanically compressed exhaust steam utilized for auxiliary heating systems, such as moisture absorption generators. Similarly, U.S. Pat. No. 4,239,603 describes the use of a turbo compressor heat engine to re-pressure a portion of the process vapor from a steam ejection vacuum cooling or drying system, thereby reducing the fuel costs associated with condensing the vapor and regenerating the steam in a boiler.
Gas turbine power plants typically extract a portion of turbine power to compress the inlet air prior to combustion, as the work extracted for compression is more than recouped by the increased combustion efficiency. It is also known in gas turbine technology, particularly turbo-prop and turbofan aircraft engines, to use a coaxial dual shaft for the turbine-compressor drive linkage, to accommodate different rotating speeds for the high and low pressure extraction/compression stages.
It is an objective of this invention to utilize a dual shaft compresser-turbine in a steam power plant to re-compress the turbine exhaust steam, and to recycle it to the turbine inlet in order to reduce the amount of condensation and steam generation required in the system cycle, thereby sacrificing some thermal efficiency in order to decrease feed water requirements and condenser size and complexity.